Polycrystalline diamond, methods of forming same, cutting elements, and earth-boring tools

ABSTRACT

A method of forming polycrystalline diamond includes providing an alloy over at least portions of a plurality of diamond particles, and subjecting the plurality of diamond particles to a high-temperature, high-pressure process to form a polycrystalline diamond material having inter-granular bonds between adjacent diamond particles. The alloy includes iridium and nickel, and a volume of the diamond particles is at least about 92% of a total volume of the alloy and the diamond particles. The polycrystalline diamond material includes at least about 92% diamond by volume. A polycrystalline diamond compact includes grains of diamond bonded to one another by inter-granular bonds and an alloy disposed within interstitial spaces between the grains of diamond. The grains of diamond occupy at least 94% by volume of the polycrystalline diamond compact. An earth-boring tool may include a bit body and such a polycrystalline diamond compact.

FIELD

Embodiments of the present disclosure relate generally topolycrystalline diamond, cutting elements, earth-boring tools, andmethod of forming such materials, cutting elements, and tools.

BACKGROUND

Earth-boring tools for forming wellbores in subterranean earthformations may include a plurality of cutting elements secured to abody. For example, fixed-cutter earth-boring rotary drill bits (alsoreferred to as “drag bits”) include a plurality of cutting elements thatare fixedly attached to a bit body of the drill bit. Similarly,roller-cone earth-boring rotary drill bits include cones that aremounted on bearing pins extending from legs of a bit body such that eachcone is capable of rotating about the bearing pin on which the cone ismounted. A plurality of cutting elements may be mounted to each cone ofthe drill bit.

The cutting elements used in earth-boring tools often includepolycrystalline diamond compact (often referred to as “PDC”) cutters,which are cutting elements that include a polycrystalline diamond (PCD)material. Such polycrystalline diamond cutting elements are formed bysintering and bonding together relatively small diamond grains orcrystals under conditions of high pressure and high temperature,typically in the presence of a catalyst (such as cobalt, iron, nickel,or alloys or mixtures thereof), to form a layer of polycrystallinediamond material on a cutting element substrate. These processes areoften referred to as high-pressure, high-temperature (or “HPHT”)processes. Catalyst material is mixed with the diamond grains to reducethe amount of oxidation of diamond by oxygen and carbon dioxide duringan HPHT process and to promote diamond-to-diamond bonding.

The cutting element substrate may include a cermet material (i.e., aceramic-metal composite material) such as cobalt-cemented tungstencarbide. In such instances, the cobalt (or other catalyst material) inthe cutting element substrate may be drawn into the diamond grains orcrystals during sintering and serve as a catalyst material for forming adiamond table from the diamond grains or crystals. In other methods,powdered catalyst material may be mixed with the diamond grains orcrystals prior to sintering the grains or crystals together in an HPHTprocess.

Upon formation of a diamond table using an HPHT process, catalystmaterial may remain in interstitial spaces between the grains orcrystals of diamond in the resulting polycrystalline diamond table. Thepresence of the catalyst material in the diamond table may contribute tothermal damage in the diamond table when the cutting element is heatedduring use, due to friction at the contact point between the cuttingelement and the formation.

Traditional PDC performance relies on the catalyst alloy which sweepsthrough the compacted diamond feed during HPHT synthesis. Traditionalcatalyst alloys are cobalt-based with varying amounts of nickel,tungsten, and chromium to facilitate diamond intergrowth between thecompacted diamond material. However, in addition to facilitating theformation of diamond-to-diamond bonds during HPHT sintering, thesealloys also facilitate the formation of graphite from diamond duringdrilling. Formation of graphite can rupture diamond necking regions(i.e., grain boundaries) due to an approximate 57% volumetric expansionduring the transformation. This phase transformation is known as“back-conversion” or “reverse graphitization,” and typically occurs attemperatures approaching 600° C. to 1,200° C., near cutting temperaturesexperienced during drilling applications. This mechanism, coupled withmismatch of the coefficients of thermal expansion of the metallic phaseand diamond, is believed to account for a significant part of thegeneral performance criteria known as “thermal stability.” Fromexperimental wear conditions, back-conversion appears to dominate thethermal stability of a PDC, promoting premature degradation of thecutting edge and performance.

To reduce problems associated with different rates of thermal expansionand with back-conversion in polycrystalline diamond cutting elements,so-called “thermally stable” polycrystalline diamond (TSD) cuttingelements have been developed. A TSD cutting element may be formed byleaching the catalyst material (e.g., cobalt) out from interstitialspaces between the diamond grains in the diamond table using, forexample, an acid. Substantially all of the catalyst material may beremoved from the diamond table. TSD cutting elements in whichsubstantially all catalyst material has been leached from the diamondtable have been reported to be thermally stable up to temperatures ofabout 1,200° C. It has also been reported, however, that fully leacheddiamond tables are relatively more brittle and vulnerable to shear,compressive, and tensile stresses than are non-leached diamond tables.In an effort to provide cutting elements having diamond tables that aremore thermally stable relative to non-leached diamond tables, but thatare also relatively less brittle and vulnerable to shear, compressive,and tensile stresses relative to fully leached diamond tables, cuttingelements have been provided that include a diamond table in which only aportion of the catalyst material has been leached from the diamondtable, for example, adjacent to a cutting face of the table, and fromthe cutting face along a side surface of the table.

BRIEF SUMMARY

In some embodiments, a method of funning polycrystalline diamondincludes providing an alloy over at least portions of a plurality ofdiamond particles, and subjecting the plurality of diamond particles toa high-temperature, high-pressure process to form a polycrystallinediamond material having inter-granular bonds between adjacent diamondparticles. The alloy comprises iridium and nickel, and a volume of thediamond particles is at least about 92% of a total volume of the alloyand the diamond particles. The polycrystalline diamond materialcomprises at least about 92% diamond by volume.

In other embodiments, a method of forming polycrystalline diamondincludes providing an alloy over at least portions of a plurality ofdiamond particles, and subjecting the plurality of diamond particles toa pressure of at least 5 GPa and a temperature of at least 1,400° C. toform a porous polycrystalline diamond compact having inter-granularbonds between adjacent diamond particles. The alloy comprises nickel andat least about 10 mol % iridium.

In certain embodiments, a polycrystalline diamond compact includesgrains of diamond bonded to one another by inter-granular bonds and analloy disposed within interstitial spaces between the grains of diamond.The alloy comprises iridium and nickel, and is from about 1 mol %iridium to about 99 mol % iridium. The grains of diamond occupy at least94% by volume of the polycrystalline diamond compact. An earth-boringtool may include a bit body and such a polycrystalline diamond compact.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming what are regarded as embodiments of the presentdisclosure, various features and advantages of embodiments of thedisclosure may be more readily ascertained from the followingdescription of example embodiments of the disclosure when read inconjunction with the accompanying drawings, in which:

FIG. 1 is a partially cut-away perspective view of an embodiment of acutting element (i.e., a polycrystalline compact) including a volume ofpolycrystalline diamond on a substrate;

FIG. 2 is a simplified view illustrating how a microstructure of thepolycrystalline diamond of the cutting element of FIG. 1 may appearunder magnification;

FIG. 3 illustrates an earth-boring rotary drill bit comprising cuttingelements as described herein;

FIG. 4 is a simplified drawing of a coated particle that may be used toform a cutting element like that of FIGS. 1 and 2 in accordance withsome embodiments of methods described herein;

FIG. 5 is a simplified drawing of another coated particle that may beused to form a cutting element like that of FIGS. I and 2 in accordancewith some embodiments of methods described herein;

FIG. 6 is a simplified cross-sectional view illustrating materials usedto form the cutting element of FIG. 1 in a container in preparation forsubjecting the container to an HPHT sintering process;

FIG. 7 is a plot of carbon solubility in alloys of iridium and nickel at1 bar; and

FIG. 8 is a plot of the liquidus of alloys of iridium and nickelsaturated with carbon at 1 bar.

DETAILED DESCRIPTION

The illustrations presented herein are not actual views of anyparticular cutting elements or tools, but are merely idealizedrepresentations that are employed to describe example embodiments of thepresent disclosure. Additionally, elements common between figures mayretain the same numerical designation.

As used herein, the term “particle” means and includes any coherentvolume of solid matter having an average dimension of about 500 μm orless, whether as grains, powder, or any other type of material. Grains(e.g., crystals) and coated grains are types of particles. As usedherein. the term “nanoparticle” means and includes any particle havingan average particle diameter of about 500 nm or less. Nanoparticlesinclude grains in a polycrystalline diamond compact having an averagegrain size of about 500 nm or less.

As used herein, the term “inter-granular bond” means and includes anydirect atomic bond (e.g., covalent, ionic, metallic, etc.) between atomsin adjacent grains of material.

As used herein, the terms “nanodiamond” and “diamond nanoparticles” meanand include any single or polycrystalline or agglomeration of nanocrystalline carbon material comprising a mixture of sp-3 and sp-2 bondedcarbon wherein the individual particle or crystal, whether singular orpart of an agglomerate, is primarily made up of sp-3 bonds. Commercialnanodiamonds are typically derived from detonation sources (e.g.,ultra-dispersed diamond or UDD) and crushed sources and can be naturallyoccurring or manufactured synthetically. Naturally occurring nanodiamondincludes the natural lonsdaleite phase identified with meteoricdeposits.

As used herein, the term “polycrystalline diamond” means and includesany material comprising a plurality of diamond grains or crystals bondeddirectly together by inter-granular diamond-to-diamond bonds. Thecrystal structures of the individual grains of polycrystalline diamondmay be randomly oriented in space within the polycrystalline diamond.

As used herein, the term “polycrystalline diamond compact” means andincludes any structure comprising a polycrystalline diamond comprisinginter-granular bonds formed by a process that involves application ofpressure (e.g., compaction) to the precursor material or materials usedto form the polycrystalline diamond compact.

As used herein, the term “earth-boring tool” means and includes any typeof bit or tool used for drilling during the formation or enlargement ofa wellbore and includes, for example, rotary drill bits, percussionbits, core bits, eccentric bits, bi-center bits, reamers, mills, dragbits, roller-cone bits, hybrid bits, and other drilling bits and toolsknown in the art.

FIG. 1 illustrates a cutting element 100, which may be formed asdisclosed herein. The cutting element 100 includes a polycrystallinediamond 102. Optionally, the cutting element 100 may also include asubstrate 104 to which the polycrystalline diamond 102 may be bonded, oron which the polycrystalline diamond 102 is formed under theaforementioned HPHT conditions. For example, the substrate 104 mayinclude a generally cylindrical body of cobalt-cemented tungsten carbidematerial, although substrates of different geometries and compositionsmay also be employed. The polycrystalline diamond 102 may be in the formof a table (i.e., a layer) of polycrystalline diamond 102 on thesubstrate 104, as shown in FIG. 1. The polycrystalline diamond 102 maybe provided on (e.g., formed on or secured to) a surface of thesubstrate 104. In additional embodiments, the cutting element 100 maysimply be a volume of the polycrystalline diamond 102 having anydesirable shape, and may not include any substrate 104. The cuttingelement 100 may be referred to as “polycrystalline compact,” or, if thepolycrystalline diamond 102 includes diamond, as a “polycrystallinediamond compact.”

As shown in FIG. 2, the polycrystalline diamond 102 may includeinterspersed and inter-bonded grains forming a three-dimensional networkof diamond. Optionally, in some embodiments, the grains of thepolycrystalline diamond 102 may have a multimodal (e.g., bi-modal,tri-modal, etc.) grain size distribution. For example, thepolycrystalline diamond 102 may comprise a multi-modal grain sizedistribution as disclosed in at least one of U.S. Pat. No. 8,579,052,issued Nov. 12, 2013, and titled “Polycrystalline Compacts IncludingIn-Situ Nucleated Grains, Earth-Boring Tools Including Such Compacts,and Methods of Forming Such Compacts and Tools”; U.S. Pat. No.8,727,042, issued May 20, 2014, and titled “Polycrystalline CompactsHaving Material Disposed in Interstitial Spaces Therein, and CuttingElements Including Such Compacts”; and U.S. Pat. No. 8,496,076, issuedJul. 30, 2013, and titled “Polycrystalline Compacts IncludingNanoparticulate Inclusions, Cutting Elements and Earth-Boring ToolsIncluding Such Compacts, and Methods of Forming Such Compacts”; thedisclosures of each of which are incorporated herein in their entiretiesby this reference.

For example, in some embodiments, the polycrystalline diamond 102 mayinclude larger grains 106 and smaller grains 108. The larger grains 106and/or the smaller grains 108 may have average particle dimensions(e.g., mean diameters) of less than 0.5 mm, less than 0.1 mm, less than0.01 mm, less than 1 μm, less than 0.1 μm, or even less than 0.01 μm.That is, the larger grains 106 and smaller grains 108 may each includemicron-sized particles (grains having an average particle diameter in arange from about 1 μm to about 500 μm (0.5 mm)), submicron-sizedparticles (grains having an average particle diameter in a range fromabout 500 nm (0.5 μm) to about 1 μm), and/or nanoparticles (particleshaving an average particle diameter of about 500 nm or less). In someembodiments, the larger grains 106 may be micron-sized diamondparticles, and the smaller grains 108 may be submicron diamond particlesor diamond nanoparticles. In some embodiments, the larger grains 106 maybe submicron diamond particles, and the smaller grains 108 may bediamond nanoparticles. In other embodiments, the grains of thepolycrystalline diamond 102 may have a monomodal grain sizedistribution. The polycrystalline diamond 102 may include directinter-granular bonds 110 between the grains 106, 108, represented inFIG. 2 by dashed lines. If the grains 106, 108 are diamond particles,the direct inter-granular bonds 110 may be diamond-to-diamond bonds.Interstitial spaces are present between the inter-bonded grains 106, 108of the polycrystalline diamond 102. In some embodiments, some of theseinterstitial spaces may include voids 113 within the polycrystallinediamond 102 in which there is no solid or liquid substance (although agas, such as air, may be present in the voids). An alloy material 112may reside in a portion of the interstitial spaces unoccupied by thegrains 106, 108 of the polycrystalline diamond 102, and may be in theform of a coating around the grains 106, 108 of the polycrystallinediamond 102.

As used herein, the term “grain size” means and includes a geometricmean diameter measured from a two-dimensional section through a bulkmaterial. The geometric mean diameter for a group of particles may bedetermined using techniques known in the art, such as those set forth inErvin E. Underwood, QUANTITATIVE STEREOLOGY, 103-105 (Addison-WesleyPublishing Company, Inc., 1970), the disclosure of which is incorporatedherein in its entirety by this reference. As known in the art, theaverage grain size of grains within a microstructure may be determinedby measuring grains of the microstructure under magnification. Forexample, a scanning electron microscope (SEM), a field emission scanningelectron microscope (FESEM), or a transmission electron microscope (TEM)may be used to view or image a surface of a polycrystalline diamond 102(e.g., a polished and etched surface of the polycrystalline diamond102). Commercially available vision systems are often used with suchmicroscopy systems, and these vision systems are capable of measuringthe average grain size of grains within a microstructure.

Referring again to FIG. 2, the alloy material 112 may include a materialthat promotes the formation of inter-granular bonds 110, and in whichcarbon is soluble. For example, the alloy material may include iridiumand nickel. An alloy of iridium and nickel may exhibit a highercarbon-solubility than nickel alone, and thus may promote the formationof inter-granular bonds 110 faster than nickel alone. A plot of carbonsolubility in alloys of iridium and nickel at 1 bar is shown in FIG. 7.As the mole percentage of iridium increases (i.e., increasing along thex-axis of FIG. 7), the solubility of carbon in the alloy increases. Thecarbon solubility of carbon in some Ir—Ni alloys may be higher than thesolubility of carbon in cobalt. For example, at 1 bar, Ir—Ni alloyshaving a mole percentage of iridium greater than about 15% may have ahigher carbon solubility that cobalt.

An alloy of iridium and nickel may exhibit a liquidus (i.e., meltingpoint) between the melting points of pure iridium (2,446° C.) and purenickel (1,455° C.). For example, the alloy material 112 may beformulated to have a liquidus of less than about 2,000° C., less thanabout 1,800° C., or even less than about 1,600° C., such as about 1,550°C. or about 1,525° C. When the alloy material 112 contains carbon, theliquidus is depressed based on the concentration of carbon. For example,the liquidus of nickel saturated with carbon is about 1,326° C. at 1bar. The liquidus of iridium saturated with carbon is about 2,286° C. at1 bar. A plot of the liquidus of alloys of iridium and nickel saturatedwith carbon at 1 bar is shown in FIG. 8. As the mole percentage ofiridium increases (i.e., increasing along the x-axis of FIG. 8), theliquidus of the alloy increases.

In some embodiments, the alloy material 112 may include carbon, iridium,and nickel. That is, carbon may be dissolved in the alloy material 112.The alloy material 112 may also include other elements. The alloymaterial 112 may be formed by diffusing carbon into a precursor of thealloy material 112 during HPHT sintering, such as a binary mixture ofiridium and nickel. Because iridium and nickel appear to be infinitelysoluble in one another, the relative amounts of each may be selected toadjust the melting temperature (liquidus) of the alloy material 112, thecarbon content, carbon solubility, or any other property. By way ofnon-limiting example, the alloy material 112 may be formed from amixture containing from about 1.0 mol % iridium to about 99.0 mol %iridium, from about 5 mol % iridium to about 40 mol % iridium, fromabout 10 mol % iridium to about 35 mol % iridium, such as about 22 mol %iridium. In some embodiments, the balance of the mixture used to formthe alloy material may be substantially nickel. In other embodiments,other elements may also be included.

The alloy material 112 may have substantially similar compositions tothose of the precursor described above, but for the presence of carbonthat may have diffused into the alloy material 112 during HPHTsintering. The amount of carbon in the alloy material 112 may depend onthe solubility of carbon in the alloy material 112 at HPHT conditions.For example, the alloy material 112 may contain up to about 15 mol %carbon, such as from about 10 mol % carbon to about 14 mol % carbon. Theamount of carbon in the alloy material 112 may be higher than the carbonsolubility of conventional metal solvent catalyst metals and alloysemployed in the formation of polycrystalline diamond compacts. Forexample, cobalt, a common metal solvent catalyst for formingpolycrystalline diamond, has a carbon solubility of about 11.4 mol %carbon. In a volume of conventional polycrystalline diamond, the diamondtypically occupies less than 100% of the total volume of the diamondtable due to the inclusion of interstitial spaces. The polycrystallinediamond 102 described herein and shown in FIGS. 1 and 2, having thealloy material 112 in interstitial spaces, may exhibit a relativelyhigher volume percentage of diamond than conventional polycrystallinediamond compacts. For example, the polycrystalline diamond 102 mayinclude at least about 92% diamond by volume, as at least about 94%diamond by volume, at least about 95% diamond by volume, at least about96% diamond by volume, at least about 97% diamond by volume, or even atleast about 99% diamond by volume. In general, compacts having highervolume fractions of diamond may exhibit better wear resistance andimproved resistance to thermal degradation.

Furthermore, the interstitial spaces may include one or more voids 113,defined as volumes within the polycrystalline table in which there is nosolid or liquid material. Thus the interstitial spaces may include thevolume occupied by the alloy material 112 and the volume occupied by thevoids 113. The volume of the alloy material 112 may be less than about50% of the interstitial spaces, such as less than about 30%, less thanabout 20%, or even less than about 10% of the interstitial spaces. Insome embodiments, a majority of the voids 113 may be interconnected toform a three-dimensional open porous network that extends throughout thepolycrystalline diamond 102. In other embodiments, a majority the voids113 may be closed and isolated from one another.

Embodiments of cutting elements 100 (FIG. 1) that includepolycrystalline diamond 102 fabricated as described herein may bemounted to earth-boring tools and used to remove subterranean formationmaterial. FIG. 3 illustrates a fixed-cutter earth-boring rotary drillbit 160. The drill bit 160 includes a bit body 162. One or more cuttingelements 100 as described herein may be mounted on the bit body 162 ofthe drill bit 160. The cutting elements 100 may be brazed or otherwisesecured within pockets formed in the outer surface of the bit body 162.The polycrystalline diamond 102 may or may not be leached beforemounting on the bit body. Other types of earth-boring tools, such asroller cone bits, percussion bits, hybrid bits, reamers, etc., also mayinclude cutting elements 100 as described herein.

In some embodiments, methods of forming polycrystalline diamond mayinclude HPHT sintering of diamond particles and an alloy material toform inter-granular bonds between the diamond particles. The diamond andalloy material may be placed into contact with one another beforesintering. For example, the alloy material may be provided over grainsor particles of diamond (e.g., as a coating) before sintering. Referringnow to FIG. 4, a grain 202 of diamond may be at least partially coatedwith an alloy material 204 to form a coated grain 206. Though depictedin FIG. 4 as completely encapsulating the grain 202, the alloy material204 may cover only a portion of an exterior surface of the grain 202. Aplurality of grains 202 may be uniformly coated. In some embodiments,grains 202 may have a distribution of an amount of the alloy material204 thereon. For example, the alloy material 204 may cover an average ofat least about 30% of the surface area of grains 202 in a particlemixture to be sintered. In some embodiments, the alloy material 204 maycover an average from about 70% to about 100% of the surface area ofgrains 202 in a particle mixture to be sintered, or at least about 90%of the surface area of grains 202. The alloy material 204 may be in acontinuous formation over each grain 202, such that even if the alloymaterial 204 does not coat the entire grain 202, there may be few or no“islands” of alloy material 204 disconnected from the remainder of thealloy material 204 on the grain 202.

The alloy material 204 may be formed to have any selected thickness,although relatively thin and uniform coatings may be desirable. Forexample, the alloy material 204 may have an average thickness from about1 nanometer (nm) to about 50 nm, from about 5 nm to about 20 nm, or fromabout 10 nm to about 15 nm.

The coated grains 206 may be formed by, for example, sputtering,physical vapor deposition (PVD), chemical vapor deposition (CVD),electroplating, or any other process known in the art. In someembodiments, the coated grains 206 may be formed by a PVD coatingprocess. The PVD process may control the composition and thickness ofthe alloy material 204 better than other coating processes. Furthermore,coating by a PVD process may provide a high-purity alloy material 204 onthe grains 202 without damaging the grains 202 or the alloy material204. The alloy material 204 may be provided to a PVD system asprealloyed material or as individual commercially pure metals (e.g.,powders, billets, etc.). The PVD system may deposit the alloy material204 in a substantially uniform thickness over the grains 202 (e.g., thethickness of alloy material 204 may vary less than about 50%, less thanabout 20%, less than about 10%, or even less than about 5%).

PVD processes may occur under an initial high vacuum, such as at apressure of less than about 10⁻⁷ torn Working pressures may be varied byincreasing or decreasing argon or other inert gas flow rates. In thismanner, the deposition rates of materials (e.g., prealloyed material orindividual commercially pure elements) may be varied as desired tocontrol compositions and/or thickness. If the alloy material to bedeposited is provided in powder form, a continuously rotating apparatusmay be used in-situ during deposition for promoting uniform coatingthickness, alloy composition, and powder surface coverage. For example,grains 202 may be placed in a ball mill with grinding media or inautogenous mill without grinding media. The mill may be subjected to avacuum, and the alloy material 204 may be deposited onto the grains 202while the mill rotates.

In some embodiments, and as shown in FIG. 5, a diamond grain 212 mayinclude a non-diamond carbon coating 216 or layer, which may be referredto as a carbon shell. The non-diamond carbon coating 216 may include,for example, graphite, graphene, fullerenes, amorphous carbon, or anyother carbon phase or morphology. The alloy material 204 may be formedover the non-diamond carbon coating 216. The alloy material 204 may beformed as described above with respect to FIG. 4. Although thenon-diamond carbon coating 216 and the alloy material 204 are depictedin FIG. 5 as completely encapsulating the diamond grain 212, in otherembodiments, the non-diamond carbon coating 216 and/or the alloymaterial 204 may only partially coat the diamond grain 212. The diamondgrain 212 may include a single diamond crystal or a cluster of diamondcrystals.

The non-diamond carbon coating 216 may react with the alloy material 204to form the alloy material 112 shown in FIG. 2. In some embodiments, atleast a portion of the non-diamond carbon coating 216 may undergo achange in atomic structure during or prior to sintering. Some carbonatoms in the non-diamond carbon coating 216 may diffuse to and enter thediamond crystal structure of the diamond grain 212 (i.e., contribute tograin growth of the diamond grain 212). For example, carbon atoms fromthe non-diamond carbon coating 216 may form “necks” of diamond materialbetween adjacent diamond grains 106, 108 (FIG. 2) during sintering(i.e., non-diamond carbon may be converted to diamond). Some carbonatoms in the non-diamond carbon coating 216 may diffuse to and enter thealloy material 204, some of which may then be converted to diamond.

In some embodiments, grains 202 (FIG. 4) or and/or grains 212 (FIG. 5)may be tumbled with an inert media to break down aggregates and promoteuniform coating. Additionally, grains 202, 212 may be pretreated toreduce aggregation and improve the flow of grains 202, 212 duringcoating processes. For example, grains 202, 212 may be pretreated withhydrogen to remove oxygen-, nitrogen- and water-bearing surfaceimpurities and/or to functionalize the surfaces with methyl or methylenegroups. Additional functionalization, such as long-alkyl-chain orfluorine compounds, may be employed for nano-diamond particles. Coatedgrains 202, 212 may include monomodal nanometer- or micron-diamond feedor composite blends of nano- and micron-diamond feed having nano-diamondcompositions from about 1% by weight to about 99% by weight. Grainscoated by PVD processes may have relatively uniform coating thicknessesacross a wide particle-size range, which may more evenly distribute thealloy material 204 to locations where the alloy material 204 isbeneficial during sintering (i.e., at the contact point between adjacentgrains). Additional multimodal nanodiamond or multimodal micron-diamondfeed may also be coated and subsequently dry-blended, forming compositeblends. The final coated feed product may be sintered at HPHTconditions, as discussed in more detail below.

Referring to FIG. 6, particles 302 of diamond having an alloy materialthereon may be positioned within a container 304 (e.g., a metalcanister). The particles 302 may include, for example, grains orcrystals of diamond (e.g., diamond grit), which will ultimately form thegrains 106, 108 in the sintered polycrystalline diamond 102 (FIG. 2).The particles 302 may include, for example, the coated grains 202, 212(FIGS. 4 & 5) having the alloy material 204 formed thereon. Thecontainer 304 may include an inner cup 306 in which the particles 302may be provided. In some embodiments, a substrate 104 (e.g., as shown inFIG. 1) optionally may also be provided in the inner cup 306 over orunder the particles 302, and may ultimately be encapsulated in thecontainer 304. The container 304 may further include a top cover 308 anda bottom cover 310, which may be assembled and bonded together (e.g.,swage bonded) around the inner cup 306 with the particles 302 and theoptional substrate 104 therein.

In the container 304, the particles 302 may have a packing fraction fromabout 45% to about 99% (i.e., with a void space of between about 55% andabout 1% of the total volume), such as from about 50% to about 70%(i.e., with a void space of between about 50% and about 30% of the totalvolume).

The container 304 with the particles 302 therein may be subjected to anHPHT process to form a polycrystalline diamond (e.g., thepolycrystalline diamond 102 shown in FIG. 1). For example, the container304 may be subjected to a pressure of at least about 5.5 GPa and atemperature of at least about 1,000° C. In some embodiments, thecontainer 304 may be subjected to a pressure of at least about 6.0 GPa,or even at least about 6.5 GPa. For example, the container 304 may besubjected to a pressure from about 5.5 GPa to about 10.0 GPa, or fromabout 6.5 GPa to about 8.0 GPa. The container 304 may be subjected to atemperature of at least about 1,600° C., at least about 1,800° C., atleast about 2,000° C., or even at least about 2,500° C.

During the sintering process, the alloy material 204 deposited on thegrains 202, 212 may melt into a liquid phase. The alloy material 204 maybehave as a metal-solvent catalyst material to promote the formation ofinter-granular (e.g., diamond-to-diamond) bonds between the grains 202,212 so as to form a polycrystalline compact from the grains 202, 212.Upon completion of the sintering process and cooling below the sinteringtemperature, the alloy material 204 solidify in interstitial spacesbetween the grains 202, 212 in the polycrystalline diamond 102.

Use of an alloy material 204 as described herein may impart certainbenefits to polycrystalline diamond 102 (FIGS. 1 & 2). For example, thealloy material 204 (including iridium and nickel) may have a highercarbon solubility than conventional cobalt-based alloys. Without beingbound to any particular theory, a higher concentration of carbon in thealloy material may correspond to faster or more uniform formation ofinter-granular bonds 110. Thus, HPHT sintering may be performed forshorter periods of time or at lower pressures than sintering withconventional catalysts. During sintering, non-diamond forms of carbonmay be converted to diamond, adding to the inter-granular bonds 110.

Furthermore, because the alloy material 204 may be coated ontoindividual grains 202, 212, the alloy material 204 need not diffusethrough the entire polycrystalline diamond 102 during sintering. Thus,the mean diffusion distance (i.e., the mean distance from any individualgrain to the alloy material 204 during sintering) may be reduced from,for example 1 mm (e.g., a significant fraction of the thickness of thepolycrystalline diamond 102), to about 1 μm or even less. In someembodiments, the mean diffusion distance may about 100 nm or less.

Furthermore, use of an alloy material 204 as described herein may allowthe alloy material 204 to be provided where needed most—at the pointswhere individual grains contact one another. Thus, volumes that are freeof grains or the alloy material 204 may become voids 113 within thepolycrystalline diamond 102, and leaching may not be required to formsuch voids 113. Thus, the polycrystalline diamond 102 formed may have alower concentration of metal than conventional unleached sinteredpolycrystalline diamond compacts. Because the alloy material 204 may beplaced near the point where it is needed to form intergranular bonds,the grains 202, 212 may be packed more tightly without negativelyaffecting the sintering process. The volume fraction of diamond may berelatively higher than in conventional materials at least in partbecause the interstitial spaces may be formed relatively smaller than inconventional materials. The polycrystalline diamond 102 may be porouswhen fully sintered because the amount of alloy material 204 providedover the grains 202, 212 may be lower than the amount of alloy materialin conventional polycrystalline materials.

One advantage of using iridium as a component of the alloy material 204is that iridium may promote fine-grained microstructures, which mayfacilitate the deposition of coatings that are of thin and uniformthickness. Quality control (i.e., thickness and uniformity) may berelatively easier for alloys containing iridium than for other alloys.For example, diamond particles having grain sizes from about 10 nm toabout 0.5 μm may be coated tougher relatively uniformly through PVD withan alloy material 204 that includes iridium or an iridium alloy. Thepower, gas pressure (plasma), and deposition time may be controlled toproduce a selected composition and thickness of the alloy material 204.

By providing the alloy material 112 or a precursor thereof as a coatingover the grains 106, 108, the time and distance required to sweep thealloy material 112 through the grains 106, 108 may be reduced. Thus, thegrains 106, 108 may be provided with a lower mean free path andtherefore a higher packing fraction. This may result in relativelyhigher final (post-sintered) density of the polycrystalline diamond 102.For example, the mean free path through the grains 106, 108 may be onthe order of the diameter of the grains 106, 108 (e.g., from about 1 nmto about 20 μm) of the microstructure of the polycrystalline diamond102, rather than the order of the thickness of the polycrystallinediamond 102 (e.g., from about 1 mm to 3.5 mm) without negativelyaffecting the ability of the alloy material 112 to fill the interstitialspaces. Furthermore, the alloy material 112 may be formulated to avoidoxidation in air. Conventional diamond grains may undergoback-conversion starting at temperatures of about 750° C. in air orabout 1,200° C. in an inert atmosphere. Providing at least some of thegrains 106, 108 with a coating material thereon may limit the timeduring which the grains 106, 108 are exposed to air or other gases inthe HPHT process, thus limiting the time during which the grains 106,108 may degrade (e.g., by conversion from diamond to carbon).Furthermore, the grains 106, 108 may be more uniformly coated with thealloy material 112, and thus may be relatively more resistant todegradation than conventional polycrystalline materials.

Additional non limiting example embodiments of the disclosure aredescribed below.

Embodiment 1: A method of forming polycrystalline diamond, comprisingproviding an alloy over at least portions of a plurality of diamondparticles; and subjecting the plurality of diamond particles to ahigh-temperature, high-pressure process to form a polycrystallinediamond material having inter-granular bonds between adjacent diamondparticles. The alloy comprises iridium and nickel, and a volume of thediamond particles is at least about 92% of a total volume of the alloyand the diamond particles. The polycrystalline diamond materialcomprises at least about 92% diamond by volume.

Embodiment 2: The method of Embodiment 1, wherein providing an alloyover at least portions of a plurality of diamond particles comprisescovering at least 30% of a surface area of the diamond particles withthe alloy.

Embodiment 3: The method of Embodiment 2, wherein providing an alloyover at least portions of a plurality of diamond particles comprisescovering at least 75% of a surface area of the particles with the alloy.

Embodiment 4: The method of any of Embodiments 1 through 3, whereinproviding an alloy over at least portions of a plurality of diamondparticles comprises forming a layer of the alloy having a thickness fromabout 1 nm to about 50 nm over the diamond particles.

Embodiment 5: The method of Embodiment 4, wherein providing an alloyover at least portions of a plurality of diamond particles comprisesforming a layer of the alloy having a thickness from about 2 nm to about5 nm over the diamond particles.

Embodiment 6: The method of any of Embodiments 1 through 5, whereinproviding an alloy over at least portions of a plurality of diamondparticles comprises providing the alloy comprising about 5 mol % iridiumto about 40 mol % iridium.

Embodiment 7: The method of Embodiment 6, wherein providing an alloyover at least portions of a plurality of diamond particles comprisesproviding the alloy comprising about 10 mol % iridium to about 35 mol %iridium.

Embodiment 8: The method of any of Embodiments 1 through 7, whereinproviding an alloy over at least portions of a plurality of diamondparticles comprises formulating the alloy to consist essentially ofiridium and nickel.

Embodiment 9: The method of any of Embodiments 1 through 8, whereinproviding an alloy over at least portions of a plurality of diamondparticles comprises formulating the alloy to exhibit a liquidus of lessthan about 1,600° C. at atmospheric pressure.

Embodiment 10: The method of any of Embodiments 1 through 9, whereinproviding an alloy over at least portions of a plurality of diamondparticles comprises providing the alloy over a plurality of diamondparticles having a multi-modal particle size distribution.

Embodiment 11: The method of any of Embodiments 1 through 10, whereinproviding an alloy over at least portions of a plurality of diamondparticles comprises providing the alloy over a plurality of diamondnanoparticles.

Embodiment 12: The method of any of Embodiments 1 through 11, whereinsubjecting the plurality of diamond particles to a high-temperature,high-pressure process comprises subjecting the plurality of diamondparticles to a temperature of at least about 1,400° C. and a pressure ofat least about 5.0 GPa.

Embodiment 13: The method of any of Embodiments 1 through 12, whereinsubjecting the plurality of diamond particles to a high-temperature,high-pressure process comprises subjecting the plurality of diamondparticles to a pressure between about 6.5 GPa and 10 GPa.

Embodiment 14: The method of any of Embodiments 1 through 13, whereinproviding an alloy over at least portions of a plurality of diamondparticles comprises providing an alloy over at least portions of aplurality of diamond particles by a physical vapor deposition process.

Embodiment 15: The method of any of Embodiments 1 through 14, whereinsubjecting the plurality of diamond particles to a high-temperature,high-pressure process comprises forming the polycrystalline diamondmaterial defining at least one void without leaching the alloytherefrom.

Embodiment 16: A method of forming polycrystalline diamond, comprisingproviding an alloy over at least portions of a plurality of diamondparticles, and subjecting the plurality of diamond particles to apressure of at least 5 GPa and a temperature of at least 1,400° C. toform a porous polycrystalline diamond compact having inter-granularbonds between adjacent diamond particles. The alloy comprises nickel andat least about 10 mol % iridium.

Embodiment 17: The method of Embodiment 16, wherein providing an alloyover at least portions of a plurality of diamond particles comprisessputtering the alloy over the plurality of diamond particles.

Embodiment 18: The method of Embodiment 16 or Embodiment 17, whereinproviding an alloy over at least portions of a plurality of diamondparticles comprises covering at least 30% of a surface area of thediamond particles with the alloy.

Embodiment 19: The method of Embodiment 18, wherein providing an alloyover at least portions of a plurality of diamond particles comprisescovering at least 75% of a surface area of the particles with the alloy.

Embodiment 20: The method of any of Embodiments 16 through 19, whereinproviding an alloy over at least portions of a plurality of diamondparticles comprises forming a layer of the alloy having a thickness fromabout 1 nm to about 20 nm over the diamond particles.

Embodiment 21: The method of Embodiment 20, wherein providing an alloyover at least portions of a plurality of diamond particles comprisesforming a layer of the alloy having a thickness from about 2 nm to about5 nm over the diamond particles.

Embodiment 22: The method of any of Embodiments 16 through 21, whereinproviding an alloy over at least portions of a plurality of diamondparticles comprises providing the alloy exhibiting a liquidus of lessthan about 1,600° C. at atmospheric pressure.

Embodiment 23: The method of any of Embodiments 16 through 22, whereinproviding an alloy over at least portions of a plurality of diamondparticles comprises providing the alloy over the plurality of diamondparticles having a multi-modal particle size distribution.

Embodiment 24: The method of any of Embodiments 16 through 23, whereinsubjecting the plurality of diamond particles to a pressure of at least5 GPa and a temperature of at least 1,400° C. comprises forming apolycrystalline diamond material defining at least one void, wherein theat least one void occupies from about 1% to about 5% of a volume of thepolycrystalline diamond compact.

Embodiment 25: The method of Embodiment 24, wherein forming apolycrystalline diamond material defining at least one void comprisesforming a polycrystalline diamond material defining at least one voidwithout leaching the alloy therefrom.

Embodiment 26: The method of any of Embodiments 16 through 25, whereinproviding an alloy over at least portions of a plurality of diamondparticles comprises forming a substantially uniform layer of the alloyover the plurality of diamond particles.

Embodiment 27: A polycrystalline diamond compact, comprising a pluralityof grains of diamond bonded to one another by inter-granular bonds andan alloy disposed within interstitial spaces between the grains ofdiamond. The alloy comprises iridium and nickel, and is from about 1 mol% iridium to about 99 mol % iridium. The grains of diamond occupy atleast 92% by volume of the polycrystalline diamond compact.

Embodiment 28: The polycrystalline diamond compact of Embodiment 27,wherein the alloy exhibits a liquidus of less than about 1,600° C. atatmospheric pressure.

Embodiment 29: The polycrystalline diamond compact of Embodiment 27 orEmbodiment 28, wherein the grains of diamond comprise nanodiamond.

Embodiment 30: The polycrystalline diamond compact of any of Embodiments27 through 29, wherein the alloy is substantially free of iron andcobalt.

Embodiment 31: The polycrystalline diamond compact of any of Embodiments27 through 30, wherein the polycrystalline diamond compact comprises atleast 94% diamond by volume.

Embodiment 32: The polycrystalline diamond compact of Embodiment 31,wherein the polycrystalline diamond compact comprises at least 94%diamond by volume.

Embodiment 33: The polycrystalline diamond compact of any of Embodiments27 through 32, wherein the alloy occupies from about 10% to about 90% ofa total volume of the interstitial spaces.

Embodiment 34: The polycrystalline diamond compact of any of Embodiments27 through 33, wherein the grains of diamond exhibit a multimodalparticle size distribution.

Embodiment 35: An earth-boring tool comprising a bit body and thepolycrystalline diamond compact of any of Embodiments 27 through 34.

While the present invention has been described herein with respect tocertain illustrated embodiments, those of ordinary skill in the art willrecognize and appreciate that it is not so limited. Rather, manyadditions, deletions, and modifications to the illustrated embodimentsmay be made without departing from the scope of the invention ashereinafter claimed, including legal equivalents thereof In addition,features from one embodiment may be combined with features of anotherembodiment while still being encompassed within the scope of theinvention as contemplated by the inventors. Further, embodiments of thedisclosure have utility with different and various types andconfigurations of tools and materials.

What is claimed is:
 1. A method of forming polycrystalline diamond,comprising: providing an alloy over at least portions of a plurality ofdiamond particles, wherein the alloy comprises iridium and nickel, andwherein a volume of the diamond particles is at least about 92% of atotal volume of the alloy and the diamond particles; and subjecting theplurality of diamond particles to a high-temperature, high-pressureprocess to form a polycrystalline diamond material having inter-granularbonds between adjacent diamond particles, wherein the polycrystallinediamond material comprises at least about 92% diamond by volume.
 2. Themethod of claim 1, wherein providing an alloy over at least portions ofa plurality of diamond particles comprises covering at least 30% of asurface area of the diamond particles with the alloy.
 3. The method ofclaim 1, wherein providing an alloy over at least portions of aplurality of diamond particles comprises forming a layer of the alloyhaving a thickness from about 1 nm to about 50 nm over the diamondparticles.
 4. The method of claim 1, wherein providing an alloy over atleast portions of a plurality of diamond particles comprises providingthe alloy comprising about 5 mol % iridium to about 40 mol % iridium. 5.The method of claim 4, wherein providing an alloy over at least portionsof a plurality of diamond particles comprises providing the alloycomprising about 10 mol % iridium to about 35 mol % iridium.
 6. Themethod of claim 1, wherein providing an alloy over at least portions ofa plurality of diamond particles comprises formulating the alloy toconsist essentially of iridium and nickel.
 7. The method of claim 1,wherein providing an alloy over at least portions of a plurality ofdiamond particles comprises formulating the alloy to exhibit a liquidusof less than about 1,600° C. at atmospheric pressure.
 8. The method ofclaim 1, wherein providing an alloy over at least portions of aplurality of diamond particles comprises providing the alloy over aplurality of diamond particles having a multi-modal particle sizedistribution.
 9. The method of claim 1, wherein providing an alloy overat least portions of a plurality of diamond particles comprisesproviding the alloy over a plurality of diamond nanoparticles.
 10. Themethod of claim 1, wherein subjecting the plurality of diamond particlesto a high-temperature, high-pressure process comprises subjecting theplurality of diamond particles to a temperature of at least about 1,400°C. and a pressure of at least about 5.0 GPa.
 11. The method of claim 1,wherein subjecting the plurality of diamond particles to ahigh-temperature, high-pressure process comprises subjecting theplurality of diamond particles to a pressure between about 6.5 GPa and10 GPa.
 12. The method of claim 1, wherein providing an alloy over atleast portions of a plurality of diamond particles comprises providingan alloy over at least portions of a plurality of diamond particles by aphysical vapor deposition process.
 13. The method of claim 1, whereinsubjecting the plurality of diamond particles to a high-temperature,high-pressure process comprises forming the polycrystalline diamondmaterial defining at least one void without leaching the alloytherefrom.
 14. A polycrystalline diamond compact, comprising: aplurality of grains of diamond bonded to one another by inter-granularbonds, wherein the grains of diamond occupy at least 92% by volume ofthe polycrystalline diamond compact; and an alloy disposed withininterstitial spaces between the grains of diamond, the alloy comprisingiridium and nickel, wherein the alloy comprises from about 1 mol %iridium to about 99 mol % iridium.
 15. The polycrystalline diamondcompact of claim 14, wherein the alloy exhibits a liquidus of less thanabout 1,600° C. at atmospheric pressure.
 16. The polycrystalline diamondcompact of claim 14, wherein the alloy is substantially free of iron andcobalt.
 17. The polycrystalline diamond compact of claim 14, wherein thealloy occupies from about 10% to about 90% of a total volume of theinterstitial spaces.
 18. The polycrystalline diamond compact of claim14, wherein the alloy further comprises carbon.
 19. The polycrystallinediamond compact of claim 14, wherein the polycrystalline diamond compactis unleached.
 20. An earth-boring tool comprising: a bit body; and thepolycrystalline diamond compact of claim 14.